Replace C Binding for VixDiskLib with FFI Binding

and integrate it with DRB to allow for client/server use
Allow FFI Enum values to be exposed as constants correctly and alias VixDiskLibFFI binding class as old VixDiskLib_raw binding class
Separate VixDiskLibFFI constants so files can include them

without including executable code
Separate VixDiskLibFFI constants so files can include them

without including executable code
Major commit of new binding to VixDiskLib using FFI and DRb.
This is the demo'ed version with the additional change that
the environment variable VIXDISKLIB_BINDING is used to determine
if it will use the FFI binding or the old C binding.
This environment variable code is to be used for comparitive
testing between the two versions and will eventually be removed.
Apply Rubocop & Peer Changes to PR replacing VixDiskLib Binding with FFI

- Insure consistent indentation
- Limit number of lines per method
- Limit length of lines
- Use snake-case when naming methods & vars
- Remove incorrect comment from "ffi" line in Gemfile
- Remove ManageIQ Copyright Comments
- Remove @@connections list and locking for multiple connections per
client since this model will utilize one connection per DRb Service.
- Simplify VixDiskLib passing of Connection return value from DRb.
- Remove VdlConnection method aliasing of disconnect to release in
MiqVimBrokerMods.
- Define $vim_log in MiqVimBrokerClient test
- Don't hard code log directory.
- Add VixDiskLibServer RuboCop suggestions.
- Begin-Rescue block for DRb service handler in VixDiskLibServer
- Add list of DRb services in VixDiskLibClient to handle exit correctly
More Rubocop & Peer Review mods to PR for VixDiskLib FFI Binding

- use $LOAD_PATH instead of $:
- use recommended spacing and remove TABs
- lock around connection handling to make sure we're not exiting
- if exit has been called require another init before a new connection
VixDiskLib FFI Binding Logging Changes for Server

- Make sure the Server picks up the path for the log relative to
the path of the server instead of hard-coding it.
- When the logging methods are not passed to init format the messages
from VixDiskLib itself appropriately
Further Peer Comments from @Fryguy updated in VixDiskLib binding PR.

- Remove extraneous blank lines.
- Remove ");" in API comments copied from VixDiskLib.h file.
- Make methods private when expected.
- Remove unneeded comments (commented out code) & align other comments
- Simplify x.nil? ? nil : foo(x) construct to x && foo(x)
- Remove unnecessary server disk count hash (simple variable suffices)
- replace string concatenation with interpolation
- remove unnecessary init log arguments from client & server and mark
them as ignored by preceding the names with "_" character.
- rename confusing "binding" variable.
- Require VixDiskLibClient init to be called before connect but
do not preclude a second init call from occurring.
- Move individual classes into separate files.  This includes the
DiskInfo, SafeConnectParams, and SafeCreateParams classes from the
vixdisklib_api.rb file, and the VDDKFactory class with associated DRb
startup functionality has been separated from the original VixDiskLib
wrapper classes (VixDiskLib, VdlConnection, & VdlDisk)
Merge pull request #4 from jerryk55/replace_vix_disk_lib_with_ffi

Replace vix disk lib with ffi