[telemetry] Don't prepend python when running gsutil on POSIX.
[telemetry] Don't prepend python when running gsutil on POSIX.

We have a bot that's using a shell script as a symlink. So Telemetry should just run it as an executable, not as a Python script.

BUG=None.
TEST=None.

Review URL: https://codereview.chromium.org/1150723006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#332251}

hgl888/chromium-crosswalk,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,chuan9/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,chuan9/chromium-crosswalk,Just-D/chromium-1,chuan9/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,TheTypoMaster/chromium-crosswalk,Chilledheart/chromium,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,Chilledheart/chromium,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,hgl888/chromium-crosswalk,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Just-D/chromium-1,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk,Just-D/chromium-1,TheTypoMaster/chromium-crosswalk,Just-D/chromium-1,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,Just-D/chromium-1