Add support for special char in volume metadata

Add support for special char in volume metadata

Using special characters such as "&" in volume metadata caused SAX
parser to split text into multiple child nodes, as stated in the
specs for SAX parsers. In this case extract_text would return
'None' because text was return if there was exactly
one child node. Concatenating the values of child nodes accounts
for SAX parsers splitting contigous characters into
multiple chunks.

Change-Id: I3709789d33ff7b07eaeaf725f5183105443d0abc
Closes-Bug: #1268513