nightly: Try even more locations for finding glibc.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14481 a5019735-40e9-0310-863c-91ae7b9d1cf9
nightly: Try harder to get vendor stuff.

/etc/issue.net might just contain control chars (like \S) a generic welcome
message or omit the precise version. The newest standard is /etc/os-release
http://www.freedesktop.org/software/systemd/man/os-release.html
Otherwise there is often lsb_release
http://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/lsbrelease.html
Try those first, fall back to /etc/issue.net if neither is there.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14482 a5019735-40e9-0310-863c-91ae7b9d1cf9