Fix a typo in bookkeeper script
Fix a typo in bookkeeper script

### Motivation

Bookkeeper script is failing to start. The variable is not being interpreted as a string. Instead we trying to run this as command and failing.

```
$ ./bin/bookkeeper localbookie 3
JAVA_HOME not set, using java from PATH. (/usr/bin/java)
./bin/bookkeeper: line 149: BOOKIE_EXTRA_OPTS: command not found
./bin/bookkeeper: line 149: -Dorg.bouncycastle.fips.approved_only=true: command not found
```

### Changes

Add quotes around the variable definition.



Reviewers: Matteo Merli <mmerli@apache.org>, Enrico Olivelli <eolivelli@gmail.com>

This closes #2667 from sursingh/fix-bookkeeper-script
apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper