Fixed Travis issue on py26 with format of empty field error.

Details:

Since 2018-04-27, Travis on Python 2.6 with PACKAGE_LEVEL=latest failed
with 'Error: zero length field name in format' on all testclient .yaml files.

Comparing the Python package versions between 4/26 and 4/27 revealed
only one changed package version: httpretty has increased from 0.8.14
to 0.9.4. It turns out httpretty dropped support for Python 2.6 in
its 0.9 version, and (suspicion) seems to be using format() on
the response we provide in the testclient .yaml files.

This change limits the version of httpretty on Python 2.6 to <0.9.

Signed-off-by: Andreas Maier <maiera@de.ibm.com>

dev-requirements.txt

@@ -15,7 +15,8 @@ pytest>=3.0.7,<3.3.0; python_version == '2.6'
 pytest>=3.0.7; python_version > '2.6'
 # testfixtures 6.0.0 no longer supports py26 and fails on py26 with syntax error
 testfixtures>=4.3.3,<6.0.0
-httpretty>=0.8.14
+httpretty>=0.8.14,<0.9.1; python_version == '2.6'
+httpretty>=0.8.14; python_version > '2.6'
 lxml>=4.0.0
 requests>=2.12.4
 decorator>=4.0.11

docs/changes.rst

@@ -41,6 +41,13 @@ Released: not yet
   representation of integer key values in binary, octal or hex format
   (part of Issue #904).
 
+* Fixed an issue with running the tests on Travis CI that occurred on
+  Python 2.6 with the latest package level and that was caused by the fact
+  that a new version of the "httpretty" Python package was released that
+  had dropped support for Python 2.6. This was fixed by limiting the
+  version of httpretty to <0.9 when running on Python 2.6. Note that
+  this only affects the development environment.
+
 **Enhancements:**
 
 * Extend pywbem MOF compiler to search for dependent classes including: