RFR: 8284539: Configure --with-source-date=version fails on MacOS

[Andrew Leonard]

JDK-8282769 added support for more ISO-8601 formats, but remove handling of just a date "YYYY-MM-DD" being present, which is the case for a configure using --with-source-date=version which uses the date string from version-numbers.conf.
Also, the first date parse had an invalid format string "%FZ %TZ", with too many Zs.
This PR corrects the first date parse to parse a standard ISO-8601 Zulu date&time: "%FT%TZ"
Then it adds the final check for no time being specified.

Signed-off-by: Andrew Leonard <anleonar at redhat.com>

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Commit messages:
 - 8284539: Configure --with-source-date=version fails on MacOS

Changes: https://git.openjdk.java.net/jdk/pull/8247/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8247&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284539
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8247.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8247/head:pull/8247

PR: https://git.openjdk.java.net/jdk/pull/8247