In Windows Lua's os.tmpname() returns relative paths starting with \s,
prepend them with $TEMP to generate a valid path.
In OS X os.tmpname() returns paths in '/tmp' but they should be in
'/private/tmp'. We cannot use os_name() for platform detection because
some tests use tempname() before nvim is spawned, instead use one of the
following:
1. Set SYSTEM_NAME environment variable before calling the tests, it
is set from CMAKE_SYSTEM_NAME(i.e. uname -s or 'Windows')
2. Call uname -s
3. Assume windows
Temporary change to avoid frequent hangs on Travis macOS/OSX builds.
Hang does not occur on Quickbuild OSX (Yosemite) build.
Reverting e9061117a5 avoids the hang, but causes
more serious regressions on many more systems.
Note that the job_spec hang only happens with the gcc-4.9 Travis OSX build.
References #5002
References #5029
