RFR: 8288895: LdapContext doesn't honor set referrals limit

[rmartinc]

Fixes [JDK-8288895](https://bugs.openjdk.org/browse/JDK-8288895).

Any `LimitExceededException` now quits the referral loop.

Added class `ReferralLimitSearchTest`. It is a simple jtreg test which checks that `java.naming.ldap.referral.limit` is really enforced. The dummy ldap server always returns a referral for any search query. If the number of searches exceeds the limit, it throws an `IOException` and the test fails.


make test TEST=jtreg:jdk/com/sun/jndi/ldap/ReferralLimitSearchTest.java

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Commit messages:
 - 8288895: LdapContext doesn't honor set referrals limit

Changes: https://git.openjdk.org/jdk/pull/9256/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9256&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288895
  Stats: 183 lines in 2 files changed: 176 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/9256.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9256/head:pull/9256

PR: https://git.openjdk.org/jdk/pull/9256