Update xNew-VM -> New-xVM, increasing ease of use and discoverability

[mtboren]

Another great function by you, William. I took the opportunity to increase the ease of use of the function, and added most of the PowerShell features that we all appreciate in a standard function/cmdlet. The updates (also listed in the comments in the updated .ps1):

Updates added Jan 2018 by Matt Boren:

• improve ease of use: can get going with as few as four (4) parameters to function, now, vs. a dozen or more (by gleaning info from the values of the few mandatory parameters, and reduction in overall parameter count)
• use approved verb for function name
• add -TrustAllCert switch parameter to give user option as to whether they want to disable SSL certificate checking, instead of disabling SSL cert checking regardless
• take source VM from object from pipeline
• default to source VM name for dest VM name if no dest VM name specified
• simplify cluster/resourcepool parameters: remove need for -Cluster, and set default value for ResourcePool, so as to reduce number of parameters needed
• simplify specifying destination vCenter -- glean this info from the -VMHost object, instead of requiring user to additionally specify the name of the destination vCenter
• simplify Datacenter parameter (remove it): glean this info from the -VMHost object, too
• add pipeline support to take pertinent values from pipeline (-SourceVM)
• optimize array creation code (just assign collection of values to array variable, instead of potentially more resource-expensive array concatenation (which actually create a new, 1-item larger array for every item addition))
• get items for credential for ServiceLocatorNamePassword from destination vCenter connection object (Client.Config)
• improve new-object creation for use in CloneVM task (creation of fewer additional interim variables, clean up overall syntax)
• correct logic around upper-casing the vC UUID value (was reversed)
• improve snapshot selection (limit scope to source VM, instead of "get snapshot by name in all of source vC", which may return multiple snapshots)
• return a Task object, so that user can update task to track progress (via their own Get-Task calls)
• sort out variable naming in function (had issues where global-scope variables were used inside of the function instead of the corresponding function parameters, like $destVCConn was being used instead of the parameter $destvc)
• add -WhatIf support
• complete the comment-based help, so that Get-Help <cmdlet> will return fully useful help (with examples and whatnot), as expected

Let's discuss any of the updates. Hopefully we can make the world even that much better of a place with these feature adds! And, I put an example of the simplified syntax at the bottom of the commit.

Cheers, Matt Boren