build: fix autobuild failures on gcov upgrade

build: fix autobuild failures on gcov upgrade

Last time I ran ./autobuild.sh was on F13; and upgrading to F14
exposed these leftovers due to a newer gcov than what was in the stale
files, in the form of spurious messages that break 'make check':

+profiling:/home/remote/eblake/libvirt-tmp/tools/virsh-console.gcda:Version mismatch - expected 405R got 404R

and concluding with a bug in the autobuild.sh script itself:

./autobuild.sh: line 44: test: =: unary operator expected

* autobuild.sh: avoid syntax error on failed test
* tools/Makefile.am (CLEANFILES): Clean coverage files.