Fix version parsing for cistem package (#9260)

Adds 'code' to the list of suffixes that are excluded from version
parsing of URLs, such that if a URL contains the string
'cistem-1.0.0-beta-source-code', a version X will substitute in to
produce a URL with cistem-X-source-code ('source' was already excluded).
The 'cistem' package version is updated to make use of this (and fix
a fetching bug with the cistem package). A unit test is added to check
this parsing case.

var/spack/repos/builtin/packages/cistem/package.py

@@ -34,7 +34,7 @@ class Cistem(AutotoolsPackage):
     homepage = "https://cistem.org/"
     url      = "https://cistem.org/system/tdf/upload3/cistem-1.0.0-beta-source-code.tar.gz?file=1&type=cistem_details&id=37&force=0"
 
-    version('1.0.0', '479f395b30ad630df3cbba9c56eb29c2')
+    version('1.0.0-beta', '479f395b30ad630df3cbba9c56eb29c2')
 
     depends_on('wx@3.0.2')
     depends_on('fftw')