lintian-junit-report: Convert output to XML after parsing

First thing first, original conversion creating intermediate REXML::Text
object and then converting it to string results in a more complex
wrapper around REXML::Text::normalize, which actually does the job which
is simply translating some characters to XML entities.

Although I know which characters are going to be converted
(REXML::DocType::DEFAULT_ENTITIES which is: ", &, < and >) and those
should not make difference in the parts of output being parsed it still
feels better for me to parse raw unmodified lintian output.

So instead of converting lintian output at once this change XML-escapes
string where needed. As additional bonus original lintian margins are
kept in output (previously those were squeezed).
lintian-junit-report: Simplify matching error/warning lines
lintian-junit-report: Name test cases after lintian tags

This patch improves representation of lintian results in Jenkins. All
the lintian results are now in package called "lintian" to separate them
from other aggregated tests. The next level of grouping in Jenkins are
classes and for those package name from lintian output is used. The
spaces in package field in lintian output are preserved, as Jenkins
doesn't care about "class" names with spaces. Finally lintian tag and
arguments (i.e. rest of line) form the test case name.
lintian-junit-report: Split lintian output between test cases

This makes only the appropriate part of lintian output to go to test
case. The error line is put as is into Stacktrace (i.e. <failure> tag)
and "Standard Output" is filled in with lintian tag information (if not
disabled).
lintian-junit-report: Fix reported total time for TCs