There are two issues in fixed_ip schema and client.
1. Schema expect string in response body-
Nova had bug#1356058 for response of reserve/unreserve fixed ip APIs,
where plain text ("202 Accepted The request is accepted for processing.")
was returned in response body.
It is fixed on Nova side - Ifca3081f573407808a2196e71ac1db87180db6ec
2. Return value of reserve_fixed_ip client method-
In Fixed ip service client, reserve_fixed_ip method does not
return the response body.
As per consistency in service client interfaces, this method should
return the response value even that is empty body.
Those were fixed in Tempest but did not get sync in lib.
-I098ee0d1fa3056f8cfb0654e2b8fd3bf75fb3e2c
-I2cb1ef8dacd1994576656cfb108dd2eef2fbd988
Change-Id: I27b8d2165188ee069f5d8d22c0426f2c748f80c8
2a6da4a5cd