Fix findbugs issues in DefaultCertificateClient#handleCase

    FindBugs :
 
       module:hadoop-hdds/common
       Incompatible bit masks in (e & 0x2 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.DefaultCertificateClient.handleCase(DefaultCertificateClient$InitCase) At DefaultCertificateClient.java:& 0x2 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.DefaultCertificateClient.handleCase(DefaultCertificateClient$InitCase) At DefaultCertificateClient.java:[line 529]
       Incompatible bit masks in (e & 0x4 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.DefaultCertificateClient.handleCase(DefaultCertificateClient$InitCase) At DefaultCertificateClient.java:& 0x4 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.DefaultCertificateClient.handleCase(DefaultCertificateClient$InitCase) At DefaultCertificateClient.java:[line 529]
       Found reliance on default encoding in org.apache.hadoop.hdds.security.x509.certificate.client.DefaultCertificateClient.validateKeyPair(PublicKey):in org.apache.hadoop.hdds.security.x509.certificate.client.DefaultCertificateClient.validateKeyPair(PublicKey): String.getBytes() At DefaultCertificateClient.java:[line 587]
       Incompatible bit masks in (e & 0x2 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.OMCertificateClient.handleCase(DefaultCertificateClient$InitCase) At OMCertificateClient.java:& 0x2 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.OMCertificateClient.handleCase(DefaultCertificateClient$InitCase) At OMCertificateClient.java:[line 95]
       Incompatible bit masks in (e & 0x4 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.OMCertificateClient.handleCase(DefaultCertificateClient$InitCase) At OMCertificateClient.java:& 0x4 == 0x1) yields a constant result in org.apache.hadoop.hdds.security.x509.certificate.client.OMCertificateClient.handleCase(DefaultCertificateClient$InitCase) At OMCertificateClient.java:[line 95]