add new mysql-lvm plugin implementation

This derives from the new base LVMSnapshot plugin in holland-lvm
add new mylvmdump plugin implementation
remove legacy plugin code
update entrypoints in holland-mysql-lvm
rename mysql-lvm configspec

- renamed mysql-lvm.configspec -> mylvmsnapshot.configspec
- symlinked mysql-lvm.configpsec -> mylvmsnapshot.configspec

This is done to cleanup the naming conventions and support legacy
behavior.
import from holland.mysql.client rather than parent package

holland.mysql needs to be a namespace package, and we can't assume
any symbols are there, so that we can split packages in the
holland.mysql namespace across separately distributed packages.
add mylvmsnapshot to mysql-lvm's entrypoints
make holland.mysql a namespace package
tag holland.mysql as a namespace package in holland-mysql-lvm
add declare_namespace() to holland.mysql package
fix imports in mylvmdump.util
override plugin aliases in mylvmdump

previously this was inheriting from mylvmsnapshot and
confusing list-plugins output
fix incorrect holland.core formatting method
tweak list-plugins to remain pretty even with the longer lvm plugin names
fixed multiple bugs in LogicalVolume.parse_snapshot_size

- various typos
- missing import of parse_bytes from holland.core.util.path
- missing parameters to log messages
do not suppress bin-log-position with file-per-table
ensure file-per-table dumps the CREATE DATABASE statement per db

- This ensures the character set is captured - we may want to
  grab additional information here in the future.
don't hard-set the plugin name in mylvmsnapshot

- previously always reset to mysql-lvm to ensure we read the right
  configspec.  This is no longer necessary
add missing path_owner improt

- new method to calculate the right mysql user to run mysqld as