Adjust tests for monitoring Cabal files to cover more cases

Without this change, Edward's original patch to monitor the contents of
Cabal files wouldn't actually be needed to make the test pass.

Originally the test only covered the case of specifying a package by a
glob that matches a .cabal file, and that case already worked because
the glob matching already included a monitor on the glob matches (ie
the .cabal file). What did not work was a glob that matched a
directory, since in that case we did the the glob match for
$thedir/*.cabal incorrectly, meaning that we didn't end up monitoring
the files properly (a path mismatch meant we were monitoring different
files).

cabal-install/tests/IntegrationTests/new-build/monitor_cabal_files/cabal.project

-packages: p/p.cabal q/q.cabal
+packages: p/p.cabal q/
+
+-- use both matching a .cabal file, and a dir
+-- since these are slightly different code paths