Add davcli client tests

* Refactored HTTPClient interface into its own package

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Validate status code received by davcli

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Assign Content-Length to davcli uploads

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Add Davcli in front of davcli suite names

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>