PR32150: support multiple --target_board dejagnu runs

PR32150: support multiple --target_board dejagnu runs

Reworked i-dejagnu-parser to fish out the "variations", i.e., data
from distinct --target_board=FOO{,BAR} in dejagnu logs.  These clauses
result in duplicated runs of .exp expfiles, and generally duplicated
subtest names.

Prior to this patch, some random subset of the results would get
associated with the expfile, with no variation awareness.  Now, the
variation string is added to the expfile name as a "[suffix]".  e.g.:
"gdb.gdb/test_outcomes.exp [native-gdbserver/-m32]".  Unfortunately,
this changes the analysis database naming convention, so for
consistency and testrun-to-testrun comparisons with current tooling, a
complete reindex over a testrun git repo should be considered.  It also
changes i/o traditions whereever expfiles are named.