fix home position timestamp to be the timestamp that the home was set and not when the message was sent

zeroed uninitialized fields on home_position, mavlink_rc_channels_override, mavlink_mission_item, mavlink_mission_item_int

It turns out that `sendto` does not work for TCP on Cygwin-Windows,
instead we need to use `send`. This required some refactoring since we
need to have the internet protocol and the port stored as a member
variable.

This should fix that lockstep SITL simulation was not working on
Windows.

    - sitl_gazebo in PX4/Firmware (1f9b8333): https://github.com/PX4/sitl_gazebo/commit/c90e8ad2b27b95dc0b4c45b346509477c5fa593d
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/e945745021a74ae45695a624dfc114a5c7bbd6bc
    - Changes: https://github.com/PX4/sitl_gazebo/compare/c90e8ad2b27b95dc0b4c45b346509477c5fa593d...e945745021a74ae45695a624dfc114a5c7bbd6bc

    e945745 2018-12-26 Julian Oes - worlds: fix rate for tailsitter and plane
46a3d27 2018-12-14 Jörg Schmidt - Fix bug in groundtruth altitude calculation

    - micro-CDR in PX4/Firmware (b043cfac5e8635d9017ad6a13f45795ad6fda6fb): https://github.com/eProsima/micro-CDR/commit/8b3546e8848e4c07c16ec55730d3ad1aa94396ab
    - micro-CDR current upstream: https://github.com/eProsima/micro-CDR/commit/7a76880f90dfe702f4fa1723e22d1dcb491d7b9e
    - Changes: https://github.com/eProsima/micro-CDR/compare/8b3546e8848e4c07c16ec55730d3ad1aa94396ab...7a76880f90dfe702f4fa1723e22d1dcb491d7b9e

    7a76880 2018-12-11 Julián Bermúdez Ortega - Badges (#24)

    - nuttx in PX4/Firmware (faf082fa1876b3f96ff9c07fc91ab8211d274c60): https://github.com/PX4/NuttX/commit/c225d4a691ef4572839b19635a84f2d9bf07ea74
    - nuttx current upstream: https://github.com/PX4/NuttX/commit/c225d4a691ef4572839b19635a84f2d9bf07ea74
    - Changes: https://github.com/PX4/NuttX/compare/c225d4a691ef4572839b19635a84f2d9bf07ea74...c225d4a691ef4572839b19635a84f2d9bf07ea74

- the flash-backend is selected by specifying nullptr as file or -1 as fd
- the default file is nullptr, and thus the FLASH
- 'param select' has no effect, FLASH is always the default

Thus there should be no functional change to existing setups.

Not all boards have an SD card.

This is a *breaking* change and requires a bootloader change.

Setting PWM_DISARMED to 0 results in no PWM output to the ESC for the pusher motor.
Most ESCs start beeping endless in short intervals if they don't get a signal.
I remove changing this parameter which is 900 by default to always command the motor to stand still.

Now that the lockstep changes are merged to master.

Now that this is merged to master in jMAVSim.

This is just because the branch got merged.

It seems that the hysteresis test fails every now and then, presumably
due to timing issues. The tests needs some improvements, e.g. isolating
it from the system time.

It turns out the noise of the airspeed depends on the least significant
bit of time which is now always 0 because time is quite regular with
lockstep. Therefore, we need a better source for the randomness. I chose
to use the sign of the y-gyro and it seems to work.

This should fix a race because the use of future/promise wasn't done in
a thread-safe way.

An include was missing.

This fixes a HITL bug and uses promise/future instead of sleeping.

This brings build fixes for Gazebo 7.

For the non-lockstep case we want to use CLOCK_MONOTONIC if possible.

This means that we can use the normal host scheduling (not lockstep) for
the unit tests.

In the future we might add unit tests using lockstep as well.

Instead of using the define __PX4_POSIX_SITL it makes more sense to have
a define just to determine if the lockstep scheduler should be used.

The -t argument had been deleted because I didn't realize that it was
actually being used. Therefore, this brings it back and we now use -c
for TCP.

This fixes all world files at 250 Hz simulation rate.