[tfs] Allow overriding tf.cmd location

Review Request #7999 — Created Feb. 25, 2016 and submitted — Latest diff uploaded

Information

RBTools
master

Reviewers

Allow an environment variable to specify location of tf.cmd for rbtools.
This will allow tf commands from visual studio 2013+ to work alongside
an installation of Team Explorer Everywhere.

Before:

C:\>rbt post -d
>>> RBTools 0.8 alpha 0 (dev)
>>> Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:32:19) [MSC v.1500 32 bit (Intel)]
>>> Running on Windows-10-10.0.10586
Checking location "%RBT_TF_PATH%\tf.cmd"
Caught OSError: [Error 2] The system cannot find the file specified

After:

C:\>rbt post -d
>>> RBTools 0.8 alpha 0 (dev)
>>> Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:32:19) [MSC v.1500 32 bit (Intel)]
>>> Running on Windows-10-10.0.10586
Checking location C:\Program Files (x86)\TEE-CLC-14.0.2\tf.cmd
Using location C:\Program Files (x86)\TEE-CLC-14.0.2\tf.cmd
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