tests: more uses of the 'unindent' subroutine

tests: more uses of the 'unindent' subroutine

* tests/backcompat.test: Prefer `unindent' over plain `cat' for
here documents created from within a loop of if/else body.
* tests/backcompat2.test: Likewise.
* tests/backcompat4.test: Likewise.
* tests/init.test: Likewise.
* tests/instmany.test: Likewise.
* tests/instmany-mans.test: Likewise.
* tests/instmany-python.test: Likewise.
* tests/missing5.test: Likewise.
* tests/parallel-am2.test : Likewise.
* tests/parallel-am3.test : Likewise.
* tests/pr307.test: Likewise.
* tests/depend4.test: Likewise.  Since we are at it, normalize
other code formatting.
* tests/instfail-java.test: Prefer `echo' over `cat' + here-doc
inside a for loop.