VirSecret implementation, thanks @dorzheh

SecretDefineXMLFromFile and SecretDefineXML

LookupSecretByUUIDString and LookupSecretByUsage

Constants  virSecretUsageType

Free and Undefine

GetUUID and GetUUIDString

GetUsageID , GetUsageType and GetXMLDesc

Integration tests
VIR_SECRET_USAGE_TYPE_ISCSI not present in 0.9