[SPARK-4861][SQL] Refactory command in spark sql

[scwf]

Follow up for #3712.
This PR finally remove CommandStrategy and make all commands follow RunnableCommand so they can go with case r: RunnableCommand => ExecutedCommand(r) :: Nil.

One exception is the DescribeCommand of hive, which is a special case and need to distinguish hive table and temporary table, so still keep HiveCommandStrategy here.

[SparkQA]

Test build #25217 has started for PR 3948 at commit 6677766.

• This patch merges cleanly.

[SparkQA]

Test build #25217 has finished for PR 3948 at commit 6677766.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/25217/
Test FAILed.

[SparkQA]

Test build #25218 has started for PR 3948 at commit 2c62e9d.

• This patch merges cleanly.

[SparkQA]

Test build #25220 has started for PR 3948 at commit 6b48e64.

• This patch merges cleanly.

[SparkQA]

Test build #25218 has finished for PR 3948 at commit 2c62e9d.

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

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/25218/
Test PASSed.

[SparkQA]

Test build #25220 has finished for PR 3948 at commit 6b48e64.

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

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/25220/
Test PASSed.

[scwf]

/cc @marmbrus

[marmbrus]

Thanks, merging to master.