[SPARK-17281][ML][MLLib] Add treeAggregateDepth parameter for AFTSurvivalRegression

[WeichenXu123]

What changes were proposed in this pull request?

Add treeAggregateDepth parameter for AFTSurvivalRegression to keep consistent with LiR/LoR.

How was this patch tested?

Existing tests.

[SparkQA]

Test build #64536 has finished for PR 14851 at commit 7ef9d8b.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #64542 has finished for PR 14851 at commit 2eafb77.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #65722 has finished for PR 14851 at commit ae37bfd.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #65753 has finished for PR 14851 at commit 378079d.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[yanboliang]

LGTM, merged into master. Thanks!