[#3831] Error on bad lease file path

[#3831] Error on bad lease file path

/doc/examples/kea4/all-keys-netconf.json
/doc/examples/kea4/all-keys.json
/doc/examples/kea4/dhcpv4-over-dhcpv6.json
/doc/examples/kea6/all-keys-netconf.json
/doc/examples/kea6/all-keys.json
/doc/examples/kea6/dhcpv4-over-dhcpv6.json
    Remove "/tmp" from lease file names

/src/bin/admin/tests/memfile_tests.sh.in
/src/bin/dhcp4/tests/dhcp4_process_tests.sh.in
/src/bin/dhcp6/tests/dhcp6_process_tests.sh.in
    export KEA_DHCP_DATA_DIR

/src/bin/shell/tests/dhcp4_basic_auth_tests.sh.in
/src/bin/shell/tests/dhcp6_basic_auth_tests.sh.in

/src/bin/shell/tests/shell_dhcp4_process_tests.sh.in
/src/bin/shell/tests/shell_dhcp6_process_tests.sh.in

/src/bin/shell/tests/tls_dhcp4_process_tests.sh.in
/src/bin/shell/tests/tls_dhcp6_process_tests.sh.in

/src/lib/dhcpsrv/dhcpsrv_messages.*
    Replace WARN message with DHCPSRV_MEMFILE_FAILED_TO_OPEN error

/src/lib/dhcpsrv/memfile_lease_mgr.cc
    Memfile_LeaseMgr::getDefaultLeaseFilePath()
    - uses CfgMgr::getDataDir()
    Memfile_LeaseMgr::initLeaseFilePath()
     - call CfgMgr::validatePath() without try-catch
    Memfile_LeaseMgr::factory()
    - log error and rethrow

/src/lib/dhcpsrv/tests/cfgmgr_unittest.cc
    Added use of EnvVarWrapper

/src/lib/dhcpsrv/tests/memfile_lease_mgr_unittest.cc
    Updated tests
    TEST_F(MemfileLeaseMgrTest, defaultDataDir)
    TEST_F(MemfileLeaseMgrTest, dataDirEnvVarOverride)
    TEST_F(MemfileLeaseMgrTest, dataDirExplicitOveride)
    - new tests

/src/lib/testutils/Makefile.am
   Added env_var_wrapper.*