PEL: Add repository to save PELs

Create the Repository class that can save PELs in (and later retrieve
them from) the filesystem.  It provides an add() method that can add
a PEL object to the repository.

Now, when the Manager class sees an OpenBMC event log created with the
RAWPEL metadata in the AdditionalData property that points at a file
that contains a PEL, it can save that PEL.  Before the PEL is saved, the
log ID and commit timestamp fields in the PEL will be updated - the log
ID to a unique value, and the timestamp to the current time.

Change-Id: I8dbaddf0f155bcb6d40b933294ada83feb75ce53
diff --git a/test/openpower-pels/pel_utils.cpp b/test/openpower-pels/pel_utils.cpp
index 4541694..46ec8ed 100644
--- a/test/openpower-pels/pel_utils.cpp
+++ b/test/openpower-pels/pel_utils.cpp
@@ -11,6 +11,8 @@
 using namespace openpower::pels;
 
 std::filesystem::path CleanLogID::pelIDFile{};
+std::filesystem::path CleanPELFiles::pelIDFile{};
+std::filesystem::path CleanPELFiles::repoPath{};
 
 constexpr uint8_t simplePEL[] = {
     // private header section header