Change case in FindOracle.cmake

Before this change, "REQUIRED" was not respected.
Default BUILD_WITH_OCI=OFF if no ORACLE_HOME
Simplify oci's CMakeLists.txt

Require Oracle via find_package. Remove conditional on ORACLE_FOUND,
since find_package will abort if we don't have Oracle.
Never build OCI on travis
Merge pull request #589 from gadomski/default-oracle-off

Default oracle to OFF if no ORACLE_HOME