posix shell: lots of cleanup and fixes

- move posix-configs/SITL/init/{rcS,10016_iris,6011_typhoon_h480} to ROMFS/px4fmu_common/init.d-posix
  allows for easier unification, only one symlink is required.
  - rcS: add AUTOCNF support. Update scripts to match with behavior of PX4
    master (parameter values, some sitl driver got removed)
- add alias to allow 'set variable value' syntax in scripts to px4-alias.sh
- use px4_getopt
- use separate argument for the test_data directory
- append PATH from within the px4 binary: this simplifies the usage
  w/o the sitl_run.sh script.
- add 'source px4-alias.sh' to all existing sitl startup scripts
- move sitl mixers to ROMFS/px4fmu_common/mixers-sitl
  makes it easier to use existing mixers and sitl-specific ones.
- remove unused rcS_gazebo_delta_wing

cmake/configs/posix_sitl_default.cmake

@@ -148,7 +148,7 @@ set(config_module_list
 # Default config_sitl_rcS_dir (posix_sitl_default), this is overwritten later
 # for the config posix_sitl_efk2 and set again, explicitly, for posix_sitl_lpe,
 # which are based on posix_sitl_default.
-set(config_sitl_rcS_dir etc/init/rcS CACHE INTERNAL "init script dir for sitl")
+set(config_sitl_rcS_dir posix-configs/SITL/init/ekf2 CACHE INTERNAL "init script dir for sitl")
 
 set(config_sitl_viewer jmavsim CACHE STRING "viewer for sitl")
 set_property(CACHE config_sitl_viewer PROPERTY STRINGS "jmavsim;none")

cmake/posix/px4-alias.sh_in

@@ -7,6 +7,14 @@ if [ ! -n "$ZSH_VERSION" ]; then
 	shopt -s expand_aliases
 fi
 
+# Map the NuttX-style variable definition 'set <var> <value>' to something that
+# bash and alternatives understand
+set() {
+	eval $1=$2
+}
+# alternative method with an alias:
+# alias set='f(){ set -- "$1=$2"; eval "$1"; unset -f f; }; eval f'
+
 # Don't stop on errors.
 #set -e