fix(collector): no validate the app_name after parse_app_perf_counter_name

[foreverneverer]

What problem does this PR solve?

Related Coredump

#0  get_app_partition_stat (sc=sc@entry=0x3753450, rows=...) at /home/jiashuo1/work/pegasus/src/server/../shell/command_helper.h:784
#1  0x00000000004c43ad in pegasus::server::info_collector::on_app_stat (this=0x3753420) at /home/jiashuo1/work/pegasus/src/server/info_collector.cpp:136
#2  0x00007ff0d894cf61 in operator() (this=0x38d40e4) at /home/jiashuo1/app/toolchain/output/include/c++/4.8.2/functional:2464
#3  dsn::timer_task::exec (this=0x38d4014) at /home/jiashuo1/work/pegasus/rdsn/src/core/core/task.cpp:475
#4  0x00007ff0d894e059 in dsn::task::exec_internal (this=this@entry=0x38d4014) at /home/jiashuo1/work/pegasus/rdsn/src/core/core/task.cpp:180
#5  0x00007ff0d89a4c7d in dsn::task_worker::loop (this=0x3110bb0) at /home/jiashuo1/work/pegasus/rdsn/src/core/core/task_worker.cpp:211
#6  0x00007ff0d89a4e49 in dsn::task_worker::run_internal (this=0x3110bb0) at /home/jiashuo1/work/pegasus/rdsn/src/core/core/task_worker.cpp:191
#7  0x00007ff0d530f600 in std::(anonymous namespace)::execute_native_thread_routine (__p=<optimized out>) at /home/qinzuoyan/git.xiaomi/pegasus/toolchain/objdir/../gcc-4.8.2/libstdc++-v3/src/c++11/thread.cc:84
#8  0x00007ff0d5e21dc5 in start_thread () from /lib64/libpthread.so.0
#9  0x00007ff0d4a7973d in clone () from /lib64/libc.so.6

Reason

#499 add parse_app_perf_counter_name to parse perf_counter_name, but no check whether the app_name from perf_counter_name is existed in dsn::app_status::AS_AVAILABLE type apps. for example, the app was dropped and the app_name should be ignored, otherwise the code line 783 will get error result and crash at line 784.

https://github.com/XiaoMi/pegasus/blob/1a1fc190d9eac42ce359dc356483ae06d583ab8b/src/shell/command_helper.h#L781-L785

What is changed and how it works?

Check if the app_name existed.

Check List

Tests

• Manual test (add detailed scripts or steps below)
  • Deploy the latest code and run for while.
  • Make sure the app_name(for example, the temp app) has the perf-counter.
  • Drop the temp app.
  • Check if collector crash and generate core dump file after runnning for a while.
  • The result is: collector runs well and no core dump file.

Related changes

• Need to cherry-pick to the release branch after the feat: support of getting backup request perf-counter in command_helper #499 cherry-pick
• Need to be included in the release note