1. Rename run-ut.sh to run-be-ut.sh
2. Find all test files from build dir instead of declaring separately in the script
3. Add gtest output to collect the result of unit test.
The upcoming patch will use CREATE_OR_OPEN mode
This patch also remove virtual dtors to cpp file.
* Move the dtors back to env.h
Generally, placing the dtor in an `.h` file(inline) or in a `cpp` file
depends on the trade-off between code expansion and function call overhead.
The code expansion rate is closely related to the number of class members
and the inheritance level.
For the several classes here: `Env`, `ReadableFile`, and `WritableFile`
have no members and are the top level of the inheritance hierarchy, But
for now I have no obvious evidence to prove that make their dtors inline
will cause serious code expansion and more instruction cache-misses,
even if there are thousands of `ReadableFile` objects kept being created
and released during running.
Now Env has unify all environment operation, such as file operation.
However some of our old functions don't leverage it. This change unify
FileUtils::scan_dir to use Env's function.
