Merging units.proto into test_runs.proto to streamline copybara

[kdsudac]

Our copybara sync to internal openhtf removes import of units_pb2 and replaces all references with test_runs_pb2.

Making this switch to streamline and to enable reversible transformations.

---

This change is 

[kdsudac]

Not sure why the travis CI build is failing. Running unit test locally and importing directly from command line locally both work fine.

from openhtf.output.callbacks import mfg_inspector

mfg_inspector.UOM_CODE_MAP

output:

{u'': 1,
 u'2J': 80,
 u'2N': 31,
 u'2Z': 38,
 u'4K': 33,
 u'4T': 36,
 u'AD': 50,
 u'AMP': 29,
 u'B84': 32,
 u'B98': 13,
 u'C81': 61,
 u'CEL': 40,
 u'COU': 37,
 u'D82': 34,
 u'DD': 60,
 u'HTZ': 12,
 u'KEL': 41,
 u'LC': 22,
 u'M0R': 24,
 u'MBPS': 51,
 u'MBR': 81,
 u'MHZ': 11,
 u'MLT': 25,
 u'MMT': 21,
 u'MTQ': 26,
 u'MTR': 23,
 u'NDL': 3,
 u'NEW': 70,
 u'P1': 2,
 u'PX': 4,
 u'PXL': 5,
 u'RPM': 7,
 u'SEC': 10,
 u'VLT': 35,
 u'WTT': 39}

[kdsudac]

Looks like the generated protobuf codes changes with whatever version of the protobuf compiler we're using in travis CI:

``
from openhtf.output.proto import units_pb2 as openhtf_dot_output_dot_proto_dot_units__pb2

[Kenadia]

Discussed offline. The justification for the change is that the structure of the protos in output/proto/ should match the structure of the protos used by MfgInspector.