Alternative Solution: USEKWALIFY env var (2 runs: one with and one without)

[jasnow]

Alternative solution (2 runs: one with and one without) USEKWALIFY env var

Based on PR#1086:

Uses an ENV[USEKWALIFY] variable to run kwalify-checks or not.

**Unclear why it runs 3 times, only need 2. **

With USEKWALIFY="yes" rake

Finished in 2.81 seconds (files took 0.43331 seconds to load)
1280 examples, 0 failures
Finished in 29.21 seconds (files took 13.13 seconds to load)
59034 examples, 0 failures
Finished in 31.2 seconds (files took 11.68 seconds to load)
57754 examples, 0 failures

unset USEKWALIFY ; rake

Finished in 2.1 seconds (files took 5.66 seconds to load)
1280 examples, 0 failures
Finished in 32.59 seconds (files took 13.92 seconds to load)
57754 examples, 0 failures
Finished in 23.46 seconds (files took 12.28 seconds to load)
56474 examples, 0 failures

NOTE: You can find all the file with kwalify references by using this command: git grep -iEl kwalify