[FLINK-18215][conf] Add log level to JavaBashUtils log4j config

[zentol]

To allow users to differentiate between warnings and info messages.

INFO  [] - Loading configuration property: jobmanager.rpc.address, localhost
INFO  [] - Loading configuration property: jobmanager.rpc.port, 6123
INFO  [] - Loading configuration property: jobmanager.memory.process.size, 1600m
INFO  [] - Loading configuration property: taskmanager.memory.process.size, 1728m
INFO  [] - Loading configuration property: taskmanager.numberOfTaskSlots, 1
INFO  [] - Loading configuration property: parallelism.default, 1
INFO  [] - Loading configuration property: jobmanager.execution.failover-strategy, region
INFO  [] - The derived from fraction jvm overhead memory (160.000mb (167772162 bytes)) is less than its min value 192.000mb (201326592 bytes), min value will be used instead
INFO  [] - Final Master Memory configuration:
INFO  [] -   Total Process Memory: 1.563gb (1677721600 bytes)
INFO  [] -     Total Flink Memory: 1.125gb (1207959552 bytes)
INFO  [] -       Heap:             1024.000mb (1073741824 bytes)
INFO  [] -       Off-heap:         128.000mb (134217728 bytes)
INFO  [] -     JVM Metaspace:      256.000mb (268435456 bytes)
INFO  [] -     JVM Overhead:       192.000mb (201326592 bytes

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[tillrohrmann]

LGTM. +1 for merging.