Fix overly-eager euca-authorize arg interpretation

Fixes TOOLS-501
Add ip-permission.group-id to euca-describe-groups

Fixes TOOLS-500
Make userdelkey and userdelcert stop requiring -u

Fixes TOOLS-486
Fix proxy handling for euca-* commands

Requestbuilder commit a6c4d64 fixes HTTP_PROXY and HTTPS_PROXY handling
for all but euca-* commands, which rely on their own copy of the method
that was fixed.  This commit applies the fix to that copy.

To fix this problem for non-euca-* commands, use requestbuilder 0.1.x >=
0.1.1 or requestbuilder 0.2.x >= 0.2.2.

Fixes TOOLS-447 only for euca-* commands
Deal with bad parsing of boolean filter values

The bool() function evaluates every non-empty string as True, breaking
args that use that as their types.  Strictly speaking, this commit just
just sidesteps the problem for the one filter that has this problem
(block-device-mapping.delete-on-termination) by changing its type to
str.  As the server handles all filter values with plain string
comparisons this is reasonable, and, in fact, should be expected for all
filters.

In case this comes up for regular args for some reason, however, this
commit also adds an arg type called flexible_bool that properly
interprets a variety of common strings for boolean values.

Fixes TOOLS-502