Use Position class to retrive drone's current position instead of using various
getters.

Subscribing to MavLink messages through callbacks can cause queue overflow if
MavLink messages are send too often. Therefore informations are now pulled
instead of updated through message subscription.

Allow subscribers' network interface to be different from the drones' one

without this cleanup, the software integration tests of KVM were stuck
forever because unittest was waiting for the subprocess to stop.

if '-ltinfo', '-ltermcap' or '-lcurses' is set in the linker option,
sqlite3 binary wil link to system libtinfo like this:

slapsoft@tomo-node:~/shared/sqlite3/39068f3749274fa37ab3897081678816/.build/sqlite-autoconf-3370200$ ldd sqlite3
	linux-vdso.so.1 (0x00007fff6dfe6000)
	libreadline.so.8 => /opt/slapgrid/shared/readline/13387ca15e2015da77fab391a268aaa6/lib/libreadline.so.8 (0x00007f4418d7d000)
	libtinfo.so.6 => /lib/x86_64-linux-gnu/libtinfo.so.6 (0x00007f4418d40000)
	libz.so.1 => /opt/slapgrid/shared/zlib/ac3692dceab375c8e6b9c06735e5faf2/lib/libz.so.1 (0x00007f4418d1b000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f4418bd7000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f4418bd1000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f4418bad000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f44189d9000)
	libncurses.so.6 => /opt/slapgrid/shared/ncurses/13a31fd4ae4eaba4a72e42f42c997f1c/lib/libncurses.so.6 (0x00007f441897c000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f4418f5a000)

if libuuid was present on the system, python would link with it in:
lib/python3.9/lib-dynload/_uuid.cpython-39-x86_64-linux-gnu.so

if libtinfo was present on the system, readline would prefer to use it instead of libncurses

This will let a non-shared Theia (for example coming from shacache
binary) to be able to use the shared parts of a machine.

See merge request nexedi/slapos!1409