oeqa/targetcontrol.py: Separate the matching of supported image fstypes from the resulting value check.
Because we used a bb.fatal call inside the get_image_fstype classmethod, this caused problems when accessed without instantiating the object with a valid bb environment.
Separating the matching part of the classmethod(that is usable by outside scripts) from the check of the resulting value.
The matching is done within a new classmethod and the latter keeps the old method name and internal functionality, this way we don't have to change any other target controllers code.
Signed-off-by: Corneliu Stoicescu <corneliux.stoicescu@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
