Fix for server error when installing some repos.

Examples: IUC's gatk2 repository, devteam's samtools_rmdup.

When attempting to install either of those, or another repository
that has tool tests with an input parameter that does not have a
value attribute, the repository would be stuck in state 'Cloning'
and show a debug link in the log. This commit resolves that error.

lib/tool_shed/metadata/metadata_generator.py

@@ -648,8 +648,8 @@ def generate_tool_metadata( self, tool_config, tool, metadata_dict ):
                 for param_name, values in ttb.inputs.iteritems():
                     # Handle improperly defined or strange test parameters and values.
                     if param_name is not None:
-                        if values is None:
-                            # An example is the 3rd test in http://testtoolshed.g2.bx.psu.edu/view/devteam/samtools_rmdup
+                        if values in [ None, False ]:
+                            # An example is the third test in http://testtoolshed.g2.bx.psu.edu/view/devteam/samtools_rmdup
                             # which is defined as:
                             # <test>
                             #    <param name="input1" value="1.bam" ftype="bam" />