posix compatibility

- use awk instead of date for generating a random id for remsh
- use -f instead of -e for testing the existence of a file
remove use of cwd to read symlink path
remove mode change on nodetool and install upgrade escripts
Merge pull request #170 from tsloughter/master

remove use of cwd to read symlink path
Merge pull request #161 from nuex/posix

posix compatibility
Merge pull request #171 from tsloughter/non_executable_escripts

remove mode change on nodetool and install upgrade escripts
Cleanup whitespace
Change default timeout from 60 seconds to 300 seconds to help with longer upgrades. This closes #131.
Merge pull request #157 from jwilberding/timeout

Timeout
don't override release set in cmd args
Merge pull request #172 from tsloughter/default_release

don't override release set in cmd args
Update to use official 17.0 release for Travis
Merge pull request #162 from jwilberding/bump_travis

Update to use official 17.0 release for Travis
fix comments for extended script search for vm.args and sys.config
Merge pull request #174 from tsloughter/extended_script_config

fix comments for extended script search for vm.args and sys.config
resolve root dir to absolute path
Merge pull request #176 from tsloughter/root_dir

resolve root dir to absolute path
breaking change: output release to <output_dir>/<release_name>/