[Vulnerable] upgrade opencv

[Le-Zheng]

Issue Description
com.intel.analytics.bigdl:bigdl directly or transitively depends on 11 C libraries (.so). However, I noticed that some C libraries are vulnerable, containing the following CVEs:

libopencv_java320.sofrom C project opencv(version:3.2.0) exposed 18 vulnerabilities:
CVE-2019-15939, CVE-2019-14491, CVE-2019-14493, CVE-2019-14492, CVE-2017-1000450, CVE-2017-12863, CVE-2017-12862, CVE-2017-12864, CVE-2017-12604, CVE-2017-12597, CVE-2017-12606, CVE-2017-12605, CVE-2017-12598, CVE-2017-12600, CVE-2017-12599, CVE-2017-12602, CVE-2017-12601, CVE-2017-12603

Solution
Possible steps:

1. install opencv 4.2.0 wget https://github.com/opencv/opencv/archive/4.2.0.tar.gz on release environment
2. replace dependency in pom.xml https://github.com/intel-analytics/BigDL-core/blob/master/opencv/opencv-java-x86_64-linux/pom.xml#L17-L20
3. compile and mvn test UT
4. release bigdl-core 2.1.0-snapshot
5. Update bigdl-core version in BigDL-dllib. Finish the whole BigDL jenkins test

Release on mac when mac machine is recovered.

[glorysdj]

do we need to release bigdl-core 2.0.1 which will be used by bigdl 2.0.1?

[Le-Zheng]

do we need to release bigdl-core 2.0.1 which will be used by bigdl 2.0.1?

Ok. We will plan it.

[Le-Zheng]

Fix in #158