[SPARK-13076][SQL] Rename ClientInterface -> HiveClient

[rxin]

And ClientWrapper -> HiveClientImpl.

I have some followup pull requests to introduce a new internal catalog, and I think this new naming reflects better the functionality of the two classes.

[SparkQA]

Test build #50365 has finished for PR 10981 at commit 0dca45c.

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• This patch adds no public classes.

[hvanhovell]

retest this please

[SparkQA]

Test build #50383 has finished for PR 10981 at commit 0dca45c.

• This patch fails Spark unit tests.
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• This patch adds no public classes.

[SparkQA]

Test build #2474 has finished for PR 10981 at commit 0dca45c.

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

[SparkQA]

Test build #2476 has finished for PR 10981 at commit 54e7287.

• This patch fails Spark unit tests.
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• This patch adds no public classes.

[SparkQA]

Test build #50413 has finished for PR 10981 at commit 279e0b3.

• This patch fails Spark unit tests.
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• This patch adds no public classes.

[SparkQA]

Test build #2480 has finished for PR 10981 at commit 279e0b3.

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

[SparkQA]

Test build #2481 has finished for PR 10981 at commit 279e0b3.

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

[rxin]

Merging this.