Avoid dependencies but explicitly link the static library where it is
used.
This also fixes that we linked libnm-log-core into
libnm-settings-plugin-ifcfg-rh.so, which duplicated the symbols
while it should used them from NetworkManager.
"nm-test-utils.h" is a header-only, helper library for our unit tests.
It was somewhat unmotivated in "shared/nm-utils", because all tests use
it, but it was not part of a "module".
Move it to "src/libnm-glib-aux/". It fits there very well. They both
have (only) a dependency on glib.
