feat: Add support for build target CentOS 8

[jopemachine]

This PR modifies the build script to enable building the centos8 libbackend-hook binary.

Ref: lablup/backend.ai#2220

build

To build the centos8 binary, enter the following command:

❯ ./build.sh centos8.0

test

Tested by test.sh.

❯ ./test.sh centos8.0
>> Running unit tests for centos8.0 x86_64
[==========] Running 2 tests from 2 test suites.
[----------] Global test environment set-up.
[----------] 1 test from has_prefix
[ RUN      ] has_prefix.basic
[       OK ] has_prefix.basic (0 ms)
[----------] 1 test from has_prefix (0 ms total)

[----------] 1 test from cpuset_parsing
[ RUN      ] cpuset_parsing.basic
[       OK ] cpuset_parsing.basic (0 ms)
[----------] 1 test from cpuset_parsing (0 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 2 test suites ran. (0 ms total)
[  PASSED  ] 2 tests.

>> Running integration tests for centos8.0 x86_64
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from sysconf
[ RUN      ] sysconf.hooked
[       OK ] sysconf.hooked (0 ms)
[----------] 1 test from sysconf (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (0 ms total)
[  PASSED  ] 1 test.