WL#8109: InnoDB: Refactor code for general tablespaces-1

This patch refactors and cleans up InnoDB code in preparation for supporting
general tablesapces in WL#6205.

This patch is one of several smaller patches that are being pushed to trunk
separately from the main wl6205 patch in order to make it easier to review.

The changes in this patch include;
1) Refactor code that initializes, validates and handles tablespace flags and
table flags. This is done so that a SHARED and TEMPORARY flag can be added to
FSP_FLAGS by wl6205.
2) Rename functions and variables to refer less to single-table tablespaces when
they will be used in wl6205 for general tablespaces as well. Add "_for_table" to
'dict_build_tablespace' since it will be specifically for file-per-table.
3) Refactor fil_create_ibd_tablespace to allocate and free the filepath in the
caller, and other cleanup.
4) Other whitespace and comment cleanups.