adding util.py to xtrabackup plugin to find current xtrabackup version
extending 'stream' option in xtrabackup to support xbstream+tar

stream is no longer simply a boolean option, but now defaults to 'tar'
'yes' and 'no' are supported for legacy purposes
implement additional streaming options and support non-streaming xtrabackup runs
add tmpdir option to xtrabackup plugin
add additional-options option for xtrabackup plugin
add ibbackup option to xtrabackup plugin
add pre-command option to xtrabackup plugin

This is intended to allow running a schema dump with mysqldump or something
similar prior to running xtrabackup
fix handling of stdout/stderr streams when using non-streaming backups
rename holland.backup.xtrabackup.base -> holland.backup.xtrabackup.plugin
more fixes for xtrabackup output streams
fix base holland.backup.xtrabackup package plugin export
fix typos
add missing subprocess.STDOUT import
remove incorrect os.makedirs block

xtrabackup always makes its own directory and will be confused if it already
exists beforehand
cleanup xtrabackup pre-command code
add --safe-slave-backup option
fix typo and missing import
add missing process.wait()
rename pre/post/backup-failure-hook to -command

This change is meant to be more compatible with holland 2.0
which has a more sophisticated notion of a hook and to more
clearly note that these "hooks" are just running shell commands
add basic support for non-standard innodb-data-file-path in mysqldump-lvm