support/scripts/setlocalversion: fix detection of hg revision when _not_ on branch...

support/scripts/setlocalversion: fix detection of hg revision when _not_ on branch 'default'

When Buildroot is stored in a Mercurial repository on a branch other than
'default' ('master' in git terms), setlocalversion (used to populate
/etc/os-release) will incorrectly think that this is a tagged version and
will NOT print out the revision hash.

This is due to the fact that the output of 'hg id' is assumed to be
    "<revision> <tags-if-any>"
but when on a branch it actually is:
    "<revision> (<branch>) <tags-if-any>"

To let setlocalversion receive the output it expects, explicitly ask 'hg id'
to retrieve only the revision hash and any tags, ommitting any branch
information.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>