Diagnostics cmdlet update

Changes:
• IaaS and PaaS Set cmdlet now take a full XML config as described in
the schema.
• PaaS Set and New cmdlet DiagnosticsConfiguration parameter has been
renamed DiagnosticsConfigurationPath and the type is now string instead
of XmlDocument. This is to be consistent with the IaaS parameter of the
same name (this is the config).
• PaaS cmdlet Set and New StorageAccountName parameter has been replaced
by StorageContext of type AzureStorageContext. This is to be consistent
with IaaS and it is the new way of passing account credentials.
• IaaS Remove now throws a NotSupportedException as it is not fully
implemented on the rdfe side.
merging and resolving conflicts. Also fixed test
Fixed test config parameter
expose instance level of website metrics and SlotView
use official webpi feed
update documentation for new CmdLets
Merge pull request #2804 from galcho/dev

expose instance level of website metrics and SlotView
Merge pull request #2805 from yugangw-msft/sdk24feed

use official webpi feed to install test dependencies
Merge pull request #2811 from AzureRT/dev

AzureRT PR S37
Merge pull request #2800 from ericprun/dev

Diagnostics cmdlet update