Commands.SqlDatabase: Fixing a bug in the Get-AzureSqlDatabaseServiceObjective that allowed the user to encounter a Null Reference Exception.
Merge branch 'dev' of https://github.com/Azure/azure-sdk-tools into dev-bug-fix
delete existing result file before invoke mstest to avoid error for existing result file
remove result files before mstest for all targets
Merge pull request #2545 from akromm/dev-bug-fix

Dev bug fix
Merge pull request #2554 from yugangw-msft/deleteresult

Delete *.trx file before invoke mstest
Commands.SqlDatabase: Have SQL cmdlets inherit from CmdletBase so that they properly set HttpRestCallLogger.CurrentCmdlet.
Commands.SqlDatabase: Fix a bug where several cmdlets weren't adding tracing headers.
Merge pull request #2555 from dlem/dev

Fix a NullReferenceException in the SQL cmdlets and add missing tracing headers.
Merge branch 'dev' into mooncacke
Ad unit tests