when running just built fuzzer binaries inside docker, use the full path

[kcc]

.. to avoid collisions with other things in PATH, including bash builtins.
Example from nss (#316 (comment)):

testing hash
Using seed corpus: hash_seed_corpus.zip
hash -rss_limit_mb=2048 -timeout=25 -runs=32 /tmp/seed_corpus/
bash: line 0: hash: -s: invalid option
hash: usage: hash [-lr] [-p pathname] [-dt] [name ...]
ERROR: bad exit code: 2

[inferno-chromium]

a789bcc should fix it, need to verify.

[inferno-chromium]

Ok fixed it properly in f52193a and b4f6676

[inferno-chromium]

fix confirmed in https://oss-fuzz-build-logs.storage.googleapis.com/build_logs/nss/latest.txt