BUILD: Disable dbus tests when running distcheck
The dbus tests that mock an sbus server were failing when make distcheck
was ran by a user logged in through the SSSD.
The reason was that the libtool wrapper around the test library alters
the LD_LIBRARY_PATH and as a consequence, the standard getpwuid_r() calls
the dbus server performs would load the in-tree NSS library and not the
system one. The-in tree library would then attempt to talk to an in-tree
NSS socket, fail, which would fail the getpwuid_r call with an error such as:
Could not get password database information for UID of current process:
User "???" unknown or no memory to allocate password entry
This patch adds a new configure-time option called --enable-dbus-tests
that is enabled by default and disabled during distcheck. When the
option is disabled, the tests that require a mocked dbus server are not
compiled at all.