tests/sitecustomize.py

merge: use the new action based mapping introduced in mergeresult obj

Before this patch, we have good number of instances of following types:

```
for f, (m, args, msg) in mresult.actions:
    if m == ACTION_X:
        do_something
```

We iterate over the whole list and then filter for a certain action. Previous
patch introduced a action based mapping in mergeresult object. The above code
now looks like:

```
for f, args, msg in mresult.getactions([ACTION_X, ...]):
    do_something
```

Differential Revision: https://phab.mercurial-scm.org/D8831

from __future__ import absolute_import
import os

if os.environ.get('COVERAGE_PROCESS_START'):
    try:
        import coverage
        import uuid

        covpath = os.path.join(
            os.environ['COVERAGE_DIR'], 'cov.%s' % uuid.uuid1()
        )
        cov = coverage.coverage(data_file=covpath, auto_data=True)
        cov._warn_no_data = False
        cov._warn_unimported_source = False
        cov.start()
    except ImportError:
        pass