add tarball.py - deploy a mysql distribution from a binary tarball
add more utility methods to util.py

- mkdir_p - call os.makedirs and suppress EEXIST errors
- resolve_mountpoint - find a mountpoint for a path
- disk_usage - find used/available space on mountpoint
add api for loading mysql distributions by various methods
add support for downloading mysql binary tarball distributions
use new distribution api to load mysql distributions

- adds a new option --mysql-source to determine what mysql
  distribution to use.  If 'system', mysql is discovered
  from standard "system" paths as we might expect from OS
  packages.  If a mysql version, this will attempt to download a
  binary tarball on demand.
update my.sandbox.cnf template

- allow setting a basedir option
- put conditions around options that might break
  older mysql versions (table-cache vs. table-open-cache, etc)
- load innodb-plugin by default on recent mysql releases
pass --ledir to mysqld_safe in sandbox.sh
add -m short option for --mysql-source
add progress bar for download
cleanup mysql-sandbox output
allow tarball source for mysql-sandbox

- if mysql-source != 'system' and ends with a .tar.gz suffix then
  try to unpack a binary tarball; Otherwise mysql-source is treated
  as a version number and we try the network path.
cleanup README.md
add 5.7 download links
add symlink to ha_innodb_plugin.so* as needed

- this allows plugin-load = ha_innodb_plugin.so to work correctly
  for mysql 5.1 without having to track down the exact so version
fix myisam-recover vs. myisam-recover-options

- this fixes an issue with MySQL 5.7 which has deprecated unique
  option prefixes.  myisam-recover-options was introduced in 5.5.3
  and the old "myisam-recover" was removed in 5.6; bootstrap
  failures with this option otherwise
update mysql-sandbox documentation to reflect new --mysql-source option
Merge branch 'feature/mysql_sandbox_w_internets' into develop