tests: make HGCATAPULTSERVERPIPE imply HGTESTCATAPULTSERVERPIPE

I had attempted to do this before, but missed this case. This makes it so that
one can do the following to get catapult traces that include both the .t test
name (and non-hg commands run by that .t test) *and* the hg-internal tracing, in
one trace:

    HGCATAPULTSERVERPIPE=/tmp/catapult.pipe run-tests.py <args>

Without this change, we need to specify both `HG{,TEST}CATAPULTSERVERPIPE`; if
we specify just the TEST one, we only get the .t tests (no hg-internals), which
is working as intended. If we specify the non-TEST one, we only get the
hg-internals (not the rest of the .t test), which was not intended.

If you want to restore the previous behavior (just hg internals, not the stuff
from the .t tests), run like:

    HGTESTCATAPULTSERVERPIPE=/dev/null \
      HGCATAPULTSERVERPIPE=/tmp/catapult.pipe \
      run-tests.py <args>

Differential Revision: https://phab.mercurial-scm.org/D5569

tests/run-tests.py

@@ -1409,7 +1409,8 b' class TTest(Test):'
         session = str(uuid.uuid4())
         if PYTHON3:
             session = session.encode('ascii')
-        hgcatapult = os.getenv('HGTESTCATAPULTSERVERPIPE')
+        hgcatapult = os.getenv('HGTESTCATAPULTSERVERPIPE') or \
+            os.getenv('HGCATAPULTSERVERPIPE')
         def toggletrace(cmd=None):
             if not hgcatapult or hgcatapult == os.devnull:
                 return