Upgrade robotframework libraries

Upgrade robotframework libraries

The two pinned robotframework libraries have not been updated for a long
time. Upgrade the libraries to the latest stable versions:

- robotframework-requests: 0.9.3
- robotframework-sshlibrary: 3.8.0

The upgrade of robotframework-requests will expose deprecation warnings
and allow a chance to address the issues before the deprecated keywords
are removed in 1.0.

Change-Id: Ic01542568470dbf05ec88f3ee3f01b7ebeab895c
Signed-off-by: Sangwook Ha <sangwook.ha@verizon.com>