Add --enable-installed-tests=exclusive, fix installed case

The major reason to do this is that running tests *both* installed
and uninstalled in our CI is a mostly pointless waste of time.
Particularly given we have a few expensive tests.

We *do* have tests that only run uninstalled (since they require
the source code) like `test-symbols.sh`.

Hence, add `--enable-installed-tests=exclusive` to mean *only* do installed for
most tests.

We'll still have uninstalled coverage via the Travis/Debian configs, and we
could perhaps do another build with a subset of uninstalled tests, but I'm not
really concerned about it.

I'd like to do a renewed push for the InstalledTests model since
I feel it's just fundamentally better.  (`g-d-t-r` kind of sucks,
but then so does the automake runner).

Also while we're here - fix the CI to use the correct context,
which started this mess.

Closes: #837
Approved by: dbnicholson

buildutil/glibtests.m4

@@ -1,17 +1,21 @@
 dnl GLIB_TESTS
-dnl
+dnl NOTE: this file has been modified from upstream glib; see
+dnl https://github.com/ostreedev/ostree/pull/837
 
 AC_DEFUN([GLIB_TESTS],
 [
   AC_ARG_ENABLE(installed-tests,
                 AS_HELP_STRING([--enable-installed-tests],
                                [Enable installation of some test cases]),
-                [case ${enableval} in
+                [enable_installed_tests=${enableval};
+                 case ${enableval} in
                   yes) ENABLE_INSTALLED_TESTS="1"  ;;
+                  exclusive) ENABLE_INSTALLED_TESTS="1"; ENABLE_INSTALLED_TESTS_EXCLUSIVE=1 ;;
                   no)  ENABLE_INSTALLED_TESTS="" ;;
                   *) AC_MSG_ERROR([bad value ${enableval} for --enable-installed-tests]) ;;
                  esac])
   AM_CONDITIONAL([ENABLE_INSTALLED_TESTS], test "$ENABLE_INSTALLED_TESTS" = "1")
+  AM_CONDITIONAL([ENABLE_INSTALLED_TESTS_EXCLUSIVE], test "$ENABLE_INSTALLED_TESTS_EXCLUSIVE" = "1")
   AC_ARG_ENABLE(always-build-tests,
                 AS_HELP_STRING([--enable-always-build-tests],
                                [Enable always building tests during 'make all']),