Description of problem:
I noticed today that I could not run pulp-dev.py -I because my nodes.conf has the ca_path setting commented out.

Version-Release number of selected component (if applicable):
master

How reproducible:
Every time.

Steps to Reproduce:
1. Comment out all of nodes.conf.
2. Run sudo ./pulp-dev -I

Actual results:
<snip>
Traceback (most recent call last):
  File "<string>", line 2, in <module>
  File "/home/rbarlow/devel/pulp/nodes/common/pulp_node/resources.py", line 43, in node_configuration
    cfg.validate(NODE_SCHEMA)
  File "/home/rbarlow/devel/pulp/common/pulp/common/config.py", line 296, in validate
    return v.validate(self)
  File "/home/rbarlow/devel/pulp/common/pulp/common/config.py", line 360, in validate
    s.validate(section)
  File "/home/rbarlow/devel/pulp/common/pulp/common/config.py", line 476, in validate
    self.validproperty(section, property)
  File "/home/rbarlow/devel/pulp/common/pulp/common/config.py", line 494, in validproperty
    raise pe
pulp.common.config.PropertyNotFound: Required property "main.ca_path", not found

Expected results:
The ca_path should be allowed to be undefined in nodes.conf.