Fix some flaky tests

[MundaneImmortal]

Description
More than 10 tests in com.huawei.dmestore.services.DmeAccessServiceImplTest may fail due to the non-deterministic order of iteration of HashMap. Specifically, the toJson() used to convert the HashMap requestbody into a JSONString will iterate the HashMap not necessarily in the order of that of putting elements.
One can check the problem using NonDex :

mvn install -pl dmestore-service -am -DskipTests
mvn edu.illinois:nondex-maven-plugin:1.1.2:nondex -pl dmestore-service -Dtest=com.huawei.dmestore.services.DmeAccessServiceImplTest

Solution
Use LinkedHashMap instead of HashMap when initializing the variable requestbody so that it can be converted into a JSONString as desired.