all: replace most uses of quotearg_colon() with quote()

all: replace most uses of quotearg_colon() with quote()

Related to commit v8.24-61-g6796698 this provides
more consistent quoting, as quotearg_colon() defaults
to "literal" quoting by default, while quote()
provides appropriate quoting for diagnostics by default.

* gl/modules/randread: Depend on quote module rather than quotearg.
* gl/lib/randread.c: Used quote() not quotearg_colon().
* src/: Likewise.
* src/shred.c: Likewise. Also avoid unnecessary quoting
introducing overhead when wiping names.
* cfg.mk: Relax the matching expression to allow
"qname" variables as used in shred.c to satisfy the check.
* tests/: Adjust accordingly.