build: fix how we use dbus-run-session
build: fix how we use dbus-run-session

Rather than overload the TPM2_TOOLS_TEST_FIXTURES test environment
variable we use the LOG_COMPILER test variable to invoke dbus-run-session,
per dbus-run-session (1):
https://dbus.freedesktop.org/doc/dbus-run-session.1.html

Signed-off-by: Joshua Lock <9750fc34162235efa862f2505c1a01f735e97af7@intel.com>

01org/tpm2.0-tools,martinezjavier/tpm2-tools,01org/tpm2.0-tools,01org/tpm2.0-tools,martinezjavier/tpm2-tools,martinezjavier/tpm2-tools,martinezjavier/tpm2-tools