Allow user to specify headers at the command line.

Currently swift client does not allow content type to be specified
when upload an object. It does not allow a user to change content
type neither. This patch will allow a user to specify content
type by using upload command or modify the content type by using
post command.

For example:
1. To upload an object with specific content type:
swift upload -H content-type:applicaiton/xml con1 file1

2. To modify an object to a specific content type:
swift post -H content-type:application/josn con1 file1

This patch also allow a client to specify other request headers.

Change-Id: I12db83a1d465285e0906889cc67dfaa44e059568
Fixes: bug #1154621
Merge "Allow user to specify headers at the command line."