Cross-platform udevadm_settle

RHEL doens't have /sbin/udevadm. Call /sbin/udevsettle instead.
Use native method instead of shelling out
Fix typo in comment
Use df's POSIX output format

so that a mount point doesn't go to multiple lines
Use sys-filesystem instead of parsing df which might not be portable and it looks better
Remove commented out log line
Prefer Bosh::Exec when shelling out
Fix sys-filesystem version
Return string for backward compatiblity
Fix test for string values
(nitpicking) Remove rogue whitespace
ci scripts to build stemcells
make gem build_with_dep task dependant on just it's gem build task
gem updates
make script files executable
Fix bosh_agent path in MCF agent startup script.
Update gemlock
Update gemlock
Configure Travis' bundler step to use local gems
Add command to create S3 buckets from configuration