Correct the wrong rename in rhel element

There is a substitution of suffix in rhel element, like
rhel-guest-image-6.5-20140121.0.x86_64.qcow2 to
rhel-guest-image-6.5-20140121.0.x86_64.raw

The convert is correct but the substitution of the suffix is wrong.

${PARAMETER#PATTERN} will match the string from the beginning and generate rhel-guest-image-6.5-20140121.0.x86_64.qcow2.raw

We should use ${PARAMETER%PATTERN} instead, which is from the end.

Change-Id: Ic45a3f800058ea9e5d746ff543c068a54632407d
Merge "Correct the wrong rename in rhel element"