Do not install on FreeBSD
Do not install on FreeBSD

For the time being we only test if we can build bazel on FreeBSD.
While further testing will be added later, for the time being, there
is no need to install bazel on the FreeBSD slaves. Also, fix the #!-line
to be independent of the location of bash.

Change-Id: Ifc7021fe4b4795bd39c8abb4a6de129f000eb42c

bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration